Hi Dirk,
There is a lot that goes into Mono. It does not fully support the .NET 2.0 framework (as of now) and it seems almost certain that there will almost always be pieces of the 2.0 framework that are unavailable in Mono. This means that any tools (ours, or others) relying on pieces of the framework that are not there, will not work properly or will not work at all.
Mono does provide a tool to check if everything you are doing in your .NET app exists in Mono: http://www.mono-project.com/Moma
They also provide a roadmap for where they plan to go in the future: http://www.mono-project.com/Roadmap
The best that I can say for C1 and Mono is that we will consider doing compatibility testing... which would mean some basic tests to see if everything is there for our tools to work. Obviously we won't be able to test all of the ways our customers use our tools, but we can at least get some idea of how successful it might be if they tried to use them. Whether we will be able to act on the results of our testing, or whether we will even do the testing for sure, I can't say right now.